In a rapid-scan Michelson interferometer, a mirror (or other reflector) is repeatedly swept over a scan range at relatively high speed (for example, a few seconds for a 1 -cm scan). The driving force is provided by a linear electric motor or similar drive source. The movement must be extremely straight and uniform. Commercially available rapid-scan interferometers typically use an air bearing comprising a piston and cylinder with provision for an air film in order to ensure low friction. While such an arrangement has proved extremely satisfactory, it has the disadvantage that a source of dry gas must be maintained for the bearing. This represents a cost, in terms of monetary expense and inconvenience.